The Ancestral Rocky Mountains (ARM) formed a system of highlands and adja-cent basins that develo... more The Ancestral Rocky Mountains (ARM) formed a system of highlands and adja-cent basins that developed during Penn-sylvanian–earliest Permian deformation of interior western North America. The cause of this intracratonic deformation remains debated, although many have linked it to far-fi eld compression associated with the Car-boniferous–Permian Ouachita-Marathon orogeny of southern North America. The ultimate disappearance of the ARM uplifts has long been attributed to erosional bevel-ing presumed to have prevailed into the Tri-assic–Jurassic. New observations, however, indicate an abrupt and unusual termination for the largest of the ARM uplifts. Field evi-dence from paleohighlands in the central ARM of Oklahoma and Colorado indicates that Lower Permian strata onlap Pennsyl-vanian-aged faults and bury as much as 1000 m of relief atop the paleohighlands. In parts of Oklahoma and Colorado, late Ceno-zoic partial exhumation of these paleohigh-lands has revealed landscapes dating from P...
Certain micrometer-scale fractures, or microtextures, on grain surfaces are the result of specifi... more Certain micrometer-scale fractures, or microtextures, on grain surfaces are the result of specific transport processes. Accordingly, these transport-induced microtextures are used to infer depositional setting in ancient deposits. Multiple transport histories complicate the microtextural record because modification of grain surfaces can reduce or eliminate the signal of earlier transport episodes. This study utilizes scanning electron microscopy to analyze surface microtextures to assess the role of fluvial overprint on glacially derived grains along 188 km of the proglacial Chitina River, SE Alaska. Results indicate that occurrence frequency of glacially induced microtextures (i.e., straight and curved grooves, deep troughs, and crescentic gouges) negatively correlates to distance downstream, yet these microtextures persist in every sample. Conversely, occurrence frequency of fluvially induced microtextures (i.e., v-shaped cracks and edge rounding) positively correlate to distance downstream. At least in the Chitina River watershed, the ratio of fluvially to glacially induced microtextures (F/G ratio) generally records physiographic variation, including increase in fluvial signal after a major tributary confluence, and decrease downstream from the intersection of valley glaciers. These results suggest that analysis of quartz grain microtextures in ancient fluvial deposits can be used to infer glacial influence when other diagnostic sedimentologic indicators of glaciation are lacking. Other potential uses for the proxy may exist, but need to be assessed after other modern proglacial systems are studied, including: 1) estimates of distance to paleo-ice margins using the respective downstream trends of glacially or fluvially induced microtextures, and 2) paleogeography of ancient glacio-fluvial systems through F/G ratio analysis.
—the taos trough is a structurally-controlled basin formed from stresses related to the ancestral... more —the taos trough is a structurally-controlled basin formed from stresses related to the ancestral rocky Mountain orogeny. Pennsylvanian sediments derived locally from Precambrian-cored uplifts fill the basin. However, structural models proposed for the development of the basin conflict. One model proposes flexure from emplacement of crustal load via a thrust fault to the west of the basin. the other model invokes intrabasinal strain manifested in thrusts with Precambrian-cored hanging walls and a strike-slip bounding fault to the west. to test these competing models, we have accumulated detailed sedimentologic and stratigraphic data from a location within the axis of the Taos trough. Specifically, we construct a detailed composite stratigraphic column for the Holman grade area using a series of road cuts along Highway 518. Construction of the column accounts for along strike duplication of strata, covered section and broad folding in the area. the composite section is ~950 m thick and is primarily composed of shallowing upward cycles that grade upward from offshore marine mudstone to a cycle cap of lower shoreface facies, upper shoreface facies, or nonmarine facies. These cycles are best characterized as fluvio-deltaic cycles. The persistent occurrence of shallow marine and nonmarine facies at the base of the section are difficult to reconcile with a flexural basin model, which often predicts a long-term, gradual shallowing as flexural accommodation that is progressively filled. Our analysis appears to show the opposite trend, albeit inconclusive, as the interval studied does not represent the entire section.
Geological Society of America Abstracts with Programs,, 2004
... surface represents the tectonic culmination of the Ely basin and the initiation of deeper wat... more ... surface represents the tectonic culmination of the Ely basin and the initiation of deeper water sedimentation of the Hogan basin. ... Timing of the C5 unconformity and sub-unconformity architecture suggest it may be genetically related to the Ancestral Rocky Mountain tectonics ...
... This suggests that the sub-Hogan unconformity reflects a regional phase of deformation. The m... more ... This suggests that the sub-Hogan unconformity reflects a regional phase of deformation. The magnitude of the sub-Pequop lacuna varies throughout eastern Nevada suggesting regional differential uplift and erosion. Rocky Mountain (53rd) and South-Central (35th) Sections ...
Creek) that head at a divide within the canyon. The history of the canyon and its role in drainag... more Creek) that head at a divide within the canyon. The history of the canyon and its role in drainage evolution of the Colorado River system remain controversial. New mapping of both bedrock and Quaternary units as well as analyses of Quaternary deposits in and near the canyon shed light on its late Cenozoic history, and call into question whether the canyon was incised by a Cenozoic river, or merely exhumed by one. Gravels near the western mouth of Unaweep Canyon (Gateway, Colorado) exhibit a distinctive intermediate volcanic provenance recording the presence of an ancestral Gunnison River; the youngest gravels are dated to 1.46 ± 0.33 Ma. Previously documented coring within the canyon reveals a thick (locally >330 m) fi ll that includes a lacustrine succession (~140 m thick), dated to 1.4-1.3 Ma, overlain by stacked paleosols and a thick (~160 m) conglomeratic unit emplaced between 1.3 Ma and the present, in addition to a basal unit of possible late Paleozoic age. Lake formation refl ects catastrophic mass wasting in western Unaweep Canyon that blocked the ancestral Gunnison River, causing partial backfi lling of the canyon, and forcing the river to seek a lower elevation exit eastward by breaching the Mesozoic rim at the northeast end of Cactus Park (Mesa County, Colorado). Ultimately, the ancestral Gunnison River joined the lower elevation Colorado River near Grand Junction by 1.3 Ma, incising the East Creek of Unaweep Canyon during the overspilling event.
The Ancestral Rocky Mountains (ARM) formed a system of highlands and adja-cent basins that develo... more The Ancestral Rocky Mountains (ARM) formed a system of highlands and adja-cent basins that developed during Penn-sylvanian–earliest Permian deformation of interior western North America. The cause of this intracratonic deformation remains debated, although many have linked it to far-fi eld compression associated with the Car-boniferous–Permian Ouachita-Marathon orogeny of southern North America. The ultimate disappearance of the ARM uplifts has long been attributed to erosional bevel-ing presumed to have prevailed into the Tri-assic–Jurassic. New observations, however, indicate an abrupt and unusual termination for the largest of the ARM uplifts. Field evi-dence from paleohighlands in the central ARM of Oklahoma and Colorado indicates that Lower Permian strata onlap Pennsyl-vanian-aged faults and bury as much as 1000 m of relief atop the paleohighlands. In parts of Oklahoma and Colorado, late Ceno-zoic partial exhumation of these paleohigh-lands has revealed landscapes dating from P...
Certain micrometer-scale fractures, or microtextures, on grain surfaces are the result of specifi... more Certain micrometer-scale fractures, or microtextures, on grain surfaces are the result of specific transport processes. Accordingly, these transport-induced microtextures are used to infer depositional setting in ancient deposits. Multiple transport histories complicate the microtextural record because modification of grain surfaces can reduce or eliminate the signal of earlier transport episodes. This study utilizes scanning electron microscopy to analyze surface microtextures to assess the role of fluvial overprint on glacially derived grains along 188 km of the proglacial Chitina River, SE Alaska. Results indicate that occurrence frequency of glacially induced microtextures (i.e., straight and curved grooves, deep troughs, and crescentic gouges) negatively correlates to distance downstream, yet these microtextures persist in every sample. Conversely, occurrence frequency of fluvially induced microtextures (i.e., v-shaped cracks and edge rounding) positively correlate to distance downstream. At least in the Chitina River watershed, the ratio of fluvially to glacially induced microtextures (F/G ratio) generally records physiographic variation, including increase in fluvial signal after a major tributary confluence, and decrease downstream from the intersection of valley glaciers. These results suggest that analysis of quartz grain microtextures in ancient fluvial deposits can be used to infer glacial influence when other diagnostic sedimentologic indicators of glaciation are lacking. Other potential uses for the proxy may exist, but need to be assessed after other modern proglacial systems are studied, including: 1) estimates of distance to paleo-ice margins using the respective downstream trends of glacially or fluvially induced microtextures, and 2) paleogeography of ancient glacio-fluvial systems through F/G ratio analysis.
—the taos trough is a structurally-controlled basin formed from stresses related to the ancestral... more —the taos trough is a structurally-controlled basin formed from stresses related to the ancestral rocky Mountain orogeny. Pennsylvanian sediments derived locally from Precambrian-cored uplifts fill the basin. However, structural models proposed for the development of the basin conflict. One model proposes flexure from emplacement of crustal load via a thrust fault to the west of the basin. the other model invokes intrabasinal strain manifested in thrusts with Precambrian-cored hanging walls and a strike-slip bounding fault to the west. to test these competing models, we have accumulated detailed sedimentologic and stratigraphic data from a location within the axis of the Taos trough. Specifically, we construct a detailed composite stratigraphic column for the Holman grade area using a series of road cuts along Highway 518. Construction of the column accounts for along strike duplication of strata, covered section and broad folding in the area. the composite section is ~950 m thick and is primarily composed of shallowing upward cycles that grade upward from offshore marine mudstone to a cycle cap of lower shoreface facies, upper shoreface facies, or nonmarine facies. These cycles are best characterized as fluvio-deltaic cycles. The persistent occurrence of shallow marine and nonmarine facies at the base of the section are difficult to reconcile with a flexural basin model, which often predicts a long-term, gradual shallowing as flexural accommodation that is progressively filled. Our analysis appears to show the opposite trend, albeit inconclusive, as the interval studied does not represent the entire section.
Geological Society of America Abstracts with Programs,, 2004
... surface represents the tectonic culmination of the Ely basin and the initiation of deeper wat... more ... surface represents the tectonic culmination of the Ely basin and the initiation of deeper water sedimentation of the Hogan basin. ... Timing of the C5 unconformity and sub-unconformity architecture suggest it may be genetically related to the Ancestral Rocky Mountain tectonics ...
... This suggests that the sub-Hogan unconformity reflects a regional phase of deformation. The m... more ... This suggests that the sub-Hogan unconformity reflects a regional phase of deformation. The magnitude of the sub-Pequop lacuna varies throughout eastern Nevada suggesting regional differential uplift and erosion. Rocky Mountain (53rd) and South-Central (35th) Sections ...
Creek) that head at a divide within the canyon. The history of the canyon and its role in drainag... more Creek) that head at a divide within the canyon. The history of the canyon and its role in drainage evolution of the Colorado River system remain controversial. New mapping of both bedrock and Quaternary units as well as analyses of Quaternary deposits in and near the canyon shed light on its late Cenozoic history, and call into question whether the canyon was incised by a Cenozoic river, or merely exhumed by one. Gravels near the western mouth of Unaweep Canyon (Gateway, Colorado) exhibit a distinctive intermediate volcanic provenance recording the presence of an ancestral Gunnison River; the youngest gravels are dated to 1.46 ± 0.33 Ma. Previously documented coring within the canyon reveals a thick (locally >330 m) fi ll that includes a lacustrine succession (~140 m thick), dated to 1.4-1.3 Ma, overlain by stacked paleosols and a thick (~160 m) conglomeratic unit emplaced between 1.3 Ma and the present, in addition to a basal unit of possible late Paleozoic age. Lake formation refl ects catastrophic mass wasting in western Unaweep Canyon that blocked the ancestral Gunnison River, causing partial backfi lling of the canyon, and forcing the river to seek a lower elevation exit eastward by breaching the Mesozoic rim at the northeast end of Cactus Park (Mesa County, Colorado). Ultimately, the ancestral Gunnison River joined the lower elevation Colorado River near Grand Junction by 1.3 Ma, incising the East Creek of Unaweep Canyon during the overspilling event.
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